He said: I said to Abu Muhammad عليه السلام: Your grace causes shyness to me to ask you questions. May I ask you a question? He said: Yes, you may ask. I said: My master, do you have a son? He said: Yes. I then said: If anything happens to you, where would I ask about him? He replied: In Medina. (al-Kafi, Volume 1, hadith 854)